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GENERAL ANAESTHESIA

M. Attia

SVUH

Feb.2007

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General Anaesthesia (GA)

A variety of drugs are given to the patient that have different effects with the overall aim of ensuring unconsciousness, amnesia and analgesia.

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Overview

General anaesthesia is a complex procedure involving :Pre-anaesthetic assessment Administration of general anaesthetic drugs Cardio-respiratory monitoring AnalgesiaAirway management Fluid management Postoperative pain relief

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Pre-anaesthetic evaluation

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Pre-anaesthetic evaluation

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Premedication

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Induction

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Intravenous Induction Agents

Commonly used IV induction agents include Prpofol, Sodium Thiopental and Ketamine.

They modulate GABAergic neuronal transmission. (GABA is the most common inhibitory neurotransmitter in humans).

The duration of action of IV induction agents is generally 5 to 10 minutes, after which time spontaneous recovery of consciousness will occur.

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(1) Propofol Short-acting agent used for the

induction, maintenance of GA and sedation in adult patients and pediatric patients older than 3 years of age.

It is highly protein bound in vivo and is metabolised by conjugation in the liver.

Side-effects is pain on injection hypotension and transient apnea following induction

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(2) Sodium thiopental

Rapid-onset ultra-short acting barbiturate, rapidly reaches the brain and causes unconsciousness within 30–45 seconds.

The short duration of action is due to its redistribution away from central circulation towards muscle and fat

The dose for induction is 3 to 7 mg/kg. Causes hypotension, apnea and

airway obstruction

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(3) Ketamine

Ketamine is a general dissociative anaesthetic.

Ketamine is classified as an NMDA Receptor Antagonist.

The effect of Ketamine on the respiratory and circulatory systems is different . When used at anaesthetic doses, it will usually stimulate rather than depress the circulatory system.

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inhalational induction agents

The most commonly-used agent is sevoflurane because it causes less irritation than other inhaled gases.

Rapidly eliminated and allows rapid awakening.

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Maintenance

In order to prolong anaesthesia for the required duration (usually the duration of surgery), patient has to breathe a carefully controlled mixture of oxygen, nitrous oxide, and a volatile anaesthetic agent. This is transferred to the patient's brain via the lungs and the bloodstream, and the patient remains unconscious.

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Maintenance

Inhaled agents are supplemented by intravenous anaesthetics, such as opioids (usually fentanyl or morphine).

At the end of surgery the volatile anaesthetic is discontinued.

Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes depending upon the duration of surgery).

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Maintenance

Total Intra-Venous Anaesthesia (TIVA): this involves using a computer controlled syringe driver (pump) to infuse Propofol throughout the duration of surgery, removing the need for a volatile anaesthetic.

Advantages: faster recovery from anaesthesia, reduced incidence of post-operative nausea and vomiting, and absence of a trigger for malignant hyperthermia.

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Neuromuscular-blocking drugs

Block neuromuscular transmission at the neuromuscular junction.

Used as an adjunct to anesthesia to induce paralysis.

Mechanical ventilation should be available to maintain adequate respiration.

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Types of NMB

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Airway management

To maintain an open airway and enable mechanical ventilation, an endotracheal tube or laryngeal mask airways are often used.

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Monitoring

ECG Pulse oximetry (SpO2) Blood Pressure Monitoring (NIBP or IBP) Agent concentration measurement Low oxygen alarm Carbon dioxide measurement (capnography) Temperature measurement Circuit disconnect alarm

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Postoperative Analgesia

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Mortality rates Overall, about five deaths per million. Most commonly related to surgical factors or pre-

existing medical conditions ( haemorrhage, sepsis). Common causes of death directly related to

anaesthesia include:

1- aspiration of stomach contents

2- suffocation (due to inadequate airway management)

3- allergic reactions to anaesthesia

4- human error

5- equipment failure